1. Field of the Invention
This invention relates to improvements in fluid-filled power unit mount devices for elastically supporting a power unit on a vehicle body, and more particularly to the power unit mount devices provided with a device intended to exhibit greater vibration damping effect throughout all power unit operating ranges.
2. Description of Prior Art
Power unit mount devices filled with a fluid have been used extensively for elastically supporting a power unit such as an automotive internal combustion engine on a vehicle body. A variety of types of fluid-filled power unit mount devices have been proposed including one which is provided with a movable partition plate structure which is so located as to divide a cavity of a mount rubber into fluid and auxiliary chambers both filled with a fluid. The partition plate structure is formed with an orifice through which the fluid and auxiliary chambers are fluidly communicable with each other. In such a type of fluid-filled power unit mount device, a vibration damping effect is obtained for large amplitude vibration in a lower frequency range (about 5-13 Hz) by virtue of resonance vibration of the fluid mass within the orifice, and for small amplitude vibration in a high frequecy range (for example, 100-170 Hz) in which booming noise is generated by virtue of the vibration of the partition plate structure. However, the partition plate structure cannot move under vibration in a frequency range (for example, 250-300 Hz) slightly higher than the booming noise generating frequency range, thus considerably raising the dynamic spring constant of the power unit mount device as a whole. This allows high frequency fine vibration due to combustion in the power unit to be transmitted from the power unit to the vehicle body.